The traditional agricultural society generally adopts sunshine drying to desiccate crops. The harvested crops usually are spread on the road under sunshine for drying, and have to be tumbled frequently by labor power to move the dried crops at the upper side to the bottom. It takes a prolonged period of sunshine, tumbling and wind blowing to dry the crops for preservation.
However, in undesirable environments such as damp or raining weather, or a drying site is difficult to get, or time is urgent for transportation or storage, the crops are easily damped and damaged. Moreover, tumbling grains manually requires a great deal of manpower, and people working in such an environment is easily suffered from heatstroke or sunburn, and the dried crops still need manpower to put them into sacks, transport and store. It leaves a lot to be desired.
With advance of technology, drying systems dedicated for crops have been developed and available on the market. They generally are held in a storage tank. Dry air enters the storage tank from the bottom and damp is expelled from the top of the storage tank. Air is circulated in such a fashion to dry the crops. But in such a drying approach, moisture in the crops is conveyed upwards layer by layer from the bottom of the storage tank to the top, and the moving distance is lengthy and a longer time is needed. Moreover, the crops piled in the storage tank are thicker than the layer adopting the traditional sunshine drying approach, the moisture expelled from the bottom tends to be absorbed by the upper crops before moving to the top. Hence drying effect suffers and energy waste occurs. There is still room for improvement.